a. Field of the Invention
The present invention pertains generally to storage of data and more specifically to organization and management of data in fault tolerant data storage systems.
b. Description of the Background
Fault tolerant data storage systems may store data across a plurality of disc drives and may include duplicate data, parity or other information that may be employed to reconstruct data if a drive fails.
Data storage systems may employ physical addressing or virtual addressing methods. In physical addressing, a file address specifies a physical address in the storage system. In virtual addressing, a file address is an address applied to a lookup table or other metadata structure to provide an actual physical address by providing an association of the virtual file address with the physical address.
Physical addressing and virtual addressing methods have both benefits and disadvantages. For example, physically mapped systems do not require the overhead of a lookup table or other data structure, but do not allow allocation of files such that access may be more evenly distributed across a number of drives for improved performance. Similarly, virtual mapped systems may be remapped to provide higher performance, but at the expense of maintaining a more complex address table.
Data storage systems may store data in various formats including various RAID (redundant array of independent discs) levels and may support a plurality of formats simultaneously. Differing RAID levels utilize different amounts of disk space to store a file of a predetermined size. This can result in increased complexity in allocating disc space to files and in lookup table overhead and execution time in accessing files. Conversion of files from a first storage format to a second storage format may require additional complexity in allocation routines and may result in fragmentation of allocated disc space.